Having twins may seem like a dream come true for some couples struggling with infertility. However, twin pregnancies come with higher risks and complications compared to singleton pregnancies. Many couples undergoing IVF aim for a singleton pregnancy and want to avoid having twins. Luckily, there are steps you can take during an IVF cycle to reduce your chances of twins and increase your chances of a healthy single baby.
Why avoid twins in IVF?
While having twins may seem exciting, twin pregnancies are considered high-risk and come with several potential complications:
- Higher risk of preterm birth – More than 50% of twin pregnancies result in preterm delivery before 37 weeks.
- Low birth weight – The average twin pregnancy results in babies with lower birth weights than singletons.
- Pregnancy risks for mother – Conditions like gestational diabetes, preeclampsia, and cesarean section are more common with twin pregnancies.
- Higher infant mortality rate – The death rate within the first year is higher for twins compared to singletons.
- Higher risk for disabilities – Twins are more likely to be born with cerebral palsy, developmental delays, and other disabilities.
- Higher financial cost – Twin pregnancies and births lead to higher medical bills for parents due to increased monitoring, interventions, and neonatal intensive care.
- Greater strain on parents – Raising twins is more demanding physically, emotionally, and financially compared to raising one baby.
For these reasons, many doctors advise patients undergoing IVF to take steps to avoid a twin pregnancy and improve the chances of a healthy singleton birth.
What causes twins in IVF?
Twins occur when two embryos implant successfully in the uterus. There are two main reasons this happens during IVF:
1. Transferring multiple embryos
The number one cause of twins from IVF is transferring more than one embryo. Doctors have traditionally transferred two or more embryos to increase the chances of pregnancy. However, this also increases the chance of twins if more than one embryo implants.
2. Embryo splitting
Even when just one embryo is transferred, there is a small chance it may split into identical twins. This occurs in about 2-5% of IVF singleton pregnancies.
How can I prevent twins when doing IVF?
The most effective ways to avoid twins from IVF include:
Single embryo transfer (SET)
Single embryo transfer involves placing only one embryo into the uterus. This eliminates the risk of twins and improves outcomes compared to double embryo transfer. SET leads to higher singleton live birth rates in many patients under age 38.
| Embryo Transfer Approach | Twin Rate | Singleton Live Birth Rate |
|---|---|---|
| Double embryo transfer | 30% | 41% |
| Single embryo transfer | 0% | 44% |
Elective single embryo transfer (eSET)
This involves proactively planning to transfer one embryo in patients with a good prognosis. eSET prevents twins while maintaining high live birth rates. It is recommended for:
- Women under age 35
- First or second IVF cycles
- At least 2 high quality embryos available
eSET has been widely adopted as the standard of care in many European countries.
Selective single embryo transfer
In this approach, doctors and patients decide on single vs. double embryo transfer based on individual factors like embryo quality, age, and number of prior IVF attempts.
For patients with poorer prognoses, transferring two embryos may increase success rates without excessively increasing twin risks. Careful patient selection allows twin prevention while optimizing outcomes.
IVF with preimplantation genetic testing (PGT)
PGT involves screening embryos for chromosomal abnormalities before transfer. Only euploid (chromosomally normal) embryos are transferred. This makes SET more effective, as normal embryos have higher implantation potential. PGT allows transfer of one embryo with excellent chances of pregnancy while nearly eliminating twins.
Assisted hatching
This technique creates a small opening in the outer embryo shell before transfer. It may facilitate embryo attachment and increase implantation rates. Some studies show assisted hatching enables similar pregnancy success with SET compared to DET.
Double embryo transfer (if needed)
For patients over 35 or those with multiple failed IVF cycles, double embryo transfer may be preferred if SET success rates are too low. However, there are still ways to reduce twin risks:
- Avoid transferring two top-quality embryos together. Transfer one top-quality and one lesser-quality embryo.
- Only transfer cleavage stage embryos on day 3, avoid transferring two blastocysts on day 5.
- Only transfer one embryo if previous IVF resulted in twins.
Proper embryo selection helps minimize twins while supporting a healthy pregnancy.
How effective are these approaches?
Multiple studies show that these prevention strategies dramatically reduce twinning rates while achieving good pregnancy outcomes with single embryo transfer:
| Study | Patients | Strategy | Twin Rate | Singleton Live Birth Rate |
|---|---|---|---|---|
| Shapiro et al. 2011 | 3508 IVF cycles | eSET policies | 1.6% | 61.7% |
| McLernon et al. 2019 | Meta-analysis | SET vs. DET | 0% vs. 21% | 29% vs. 42% |
| Garrido et al. 2013 | 214 IVF cycles with PGT | SET with euploid embryos | 0% | 66% |
These findings confirm that following careful embryo transfer practices enables the vast majority of couples to achieve a healthy singleton pregnancy through IVF while avoiding risky twin pregnancies.
What are risks from single embryo transfer IVF?
While SET carries extremely low twin risks, potential downsides include:
- Lower pregnancy rates per transfer compared to DET, but similar rates over multiple cycles
- Possible need for additional frozen embryo transfers if first SET fails
- Higher costs if additional IVF cycles are needed for another singleton
However, most couples prefer taking these risks to avoid the greater dangers of twins. Going step-by-step with single embryo transfers gives high cumulative success rates while protecting the mother and baby.
Conclusion
Preventing twins during IVF is crucial to reduce pregnancy complications and promote the best outcomes. Single embryo transfer, along with careful patient selection, freezing extra embryos, and techniques like PGT allow maximizing the chances of a healthy singleton birth while avoiding the risks of twins and high-order multiples. If you are hoping to get pregnant through IVF, discuss a twin prevention plan with your doctor to give you and your baby the best chances for safety and success.